VulnerabilityPublished 25 Mar 2026

CVE-2026-20125: Cisco IOS · Improper Handling of Syntactically Invalid Structure

Affects Cisco IOSSource CVE Database V5

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Not known to be exploited · CVSS 7.7 High.

Data as of 30 Oct 2026, 11:52 UTC

CVSS 3.1 base score

7.7High

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.2% chance of exploitation in 30 days – higher than 21% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H

Attack Vector: Network
Attack Complexity: Low
Privileges Required: Low
User Interaction: None
Scope: Changed
Confidentiality: None
Integrity: None
Availability: High

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: Low: The attacker is authorized with (i.e., requires) privileges that provide basic user capabilities that could normally affect only settings and files owned by a user. Alternatively, an attacker with Low privileges may have the ability to cause an impact only to non-sensitive resources.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Changed: An exploited vulnerability can affect resources beyond the security scope managed by the security authority of the vulnerable component. In this case, the vulnerable component and the impacted component are different and managed by different security authorities.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 25 Mar 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 30 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Affected software

Product	Affected	Fixed in
CiscoIOS	Affected 12.2(25)EZ – 15.9(3)M12 943 affected builds	Fixed in–
CiscoCisco IOS XE Software	Affected 3.5.0E – 3.18.9SP 157 affected builds	Fixed in–

AI-suggested

Apply Cisco's official patches or software updates that address CVE-2026-20125 as soon as they become available to eliminate the vulnerability.
Restrict access to the HTTP server feature on Cisco IOS devices by disabling it if not required or limiting access to trusted management networks only.
Enforce strong authentication and credential management policies to prevent unauthorized access to devices.
Implement network segmentation and access control lists (ACLs) to limit exposure of management interfaces to untrusted networks.
Monitor network traffic for anomalous or malformed HTTP requests targeting Cisco IOS devices, using intrusion detection/prevention systems (IDS/IPS) and security information and event management (SIEM) tools.
Conduct regular audits of device configurations and user accounts to detect and remove unnecessary privileges.
Prepare incident response plans to quickly identify and recover from device reloads or outages caused by exploitation attempts.
Consider using out-of-band management channels for device administration to reduce attack surface.

Description

A vulnerability in the HTTP Server feature of Cisco IOS Software and Cisco IOS XE Software Release 3E could allow an authenticated, remote attacker to cause an affected device to reload unexpectedly, resulting in a denial of service (DoS) condition. This vulnerability is due to improper validation of user-supplied input. An attacker could exploit this vulnerability by sending malformed HTTP requests to an affected device. A successful exploit could allow the attacker to cause a watchdog timer to expire and the device to reload, resulting in a DoS condition. To exploit this vulnerability, the attacker must have a valid user account.

Impact

The primary impact of CVE-2026-20125 is a denial of service condition caused by device reloads, which can disrupt network availability and connectivity. Organizations relying on Cisco IOS devices for routing, switching, and network management could experience outages, degraded performance, or loss of critical network services. This can affect enterprise IT operations, cloud service providers, telecommunications infrastructure, and government networks. The requirement for valid authentication limits exploitation to insiders or attackers who have compromised credentials, but the low complexity and network accessibility increase risk. The widespread deployment of affected Cisco IOS versions globally means that many organizations could be impacted. Prolonged or repeated exploitation could lead to significant operational disruption, financial losses, and reputational damage. Additionally, network instability caused by unexpected device reloads could complicate incident response and recovery efforts.

References

sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ios-http-dos-sbv8XRpL (opens in a new tab)

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 25 Mar 2026, 16:31 UTC

Technical details

References

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